FIG. 1 shows a conventional spatial arrangement of a mobile device 101 and two base stations 102, 103. Each of the base stations 102, 103 transmits and receives in 360 degrees. For each base station, the 360-degree directionality may be divided into three 120-degree sectors. The mobile device 101 is located in a position such that it receives signals from both base stations 102, 103. In other words, the mobile device 101 receives transmissions from at least one of the sectors of each of the base stations 102, 103.
In the arrangement shown in FIG. 1, forward-link transmissions (from the base stations 102, 103 to the mobile device 101) are data streams divided into frames. The frames are further divided into time slots. The time slots have pilot segments and traffic segments. In 3G and 4G data transmission systems, pilot and traffic transmissions are orthogonally multiplexed together, as shown in FIGS. 2 and 3, which show a fully loaded (“active”) and idle half slot in cdma2000 EV-DO, respectively.
Sector transmissions are synchronized, i.e., pilots from different sectors interfere with each other, and traffic transmissions from different sectors interfere with each other. In the arrangement shown in FIG. 3, not all traffic segments in the forward link are occupied. Thus, whereas pilot segments in the slots are always occupied, some traffic segments can be empty. The pilot segments are used to estimate channel states that are expected to be experienced by the traffic segments, and channel state estimation often includes estimation of interference. However, for a given signal, the channel state measurements during a pilot segment may be somewhat different than the channel state experienced during the traffic transmission when one or more interfering signals have empty traffic segments. Accordingly, conventional traffic interference estimations based upon pilot signals may not be optimally precise when some sectors in interfering signals are less than fully loaded.